I think basing purely off of ping is not a great idea. I mean ping has multiple factors. it is also based off your geographical location vs the server location. The ping could be high for you, but then low for someone I. Alaska. Now in theory you could load balance, but then that would just be very costly.
I judge based on ping, uptime, pipe speed, and hops. average it all together. that is how to figure it out for you a single person. but you still have to remember all the people who are going to visit your regions.